1. The Field of the Invention
The present invention relates to the field of data transmission in a wireless network. More particularly, the present invention relates to a method and system for improving data rate transmission via a wireless transceiver optimized for voice transmission.
2. Present State of the Art
Wireless communication systems have become increasingly more prevalent and contribute greatly to the dynamic nature of modern society. Generally, wireless technology enables individuals to maintain communication contacts with fixed site stations or other mobile users. Such heavy demands on wireless communication technology have advanced the present state of the art in wireless communication to systems having very high levels of reliability and, hence, customer satisfaction. Modern, wireless communication systems have catered primarily to voice users, such as wireless users interacting with other users or systems using verbal communication. To improve customer satisfaction, therefore, wireless communication systems have been adapted to favorably facilitate verbal or voice communication.
As a result of the sprawl of wireless communication systems, additional applications of wireless communication technology have been undertaken. For example, wireless communication systems may additionally be used for the transmission of data information to and from a user such as in the case of paging and other digital transmission technologies. In the past, digital transmissions via wireless transceivers have tended to adequately accommodate the generally small amounts of digital data by employing low transmission data rates which were adequate. Transmission of substantial amounts of digital data at low data rates may congest communication channels. Data transmissions in wireless communication systems are especially impacted in analog cellular networks. In such analog systems, modems connected to analog wireless transceivers reliably transmit at around 9600 bits per second. Although these rates may be sufficient for transferring moderate amounts of data, modern applications of wireless communication networks demand additional bandwidth for satisfactory user interaction. Such wireless transfer applications include file transfers from a portable computer having a modem via a wireless transceiver.
An additional and increasingly more popular use of wireless data transmission involves wireless access of the Internet. A personal portable computer having a modem coupled to a wireless transceiver may access vast amounts of digital data from remote or mobile locations. Because of the large amount of data transferred during such activities as Internet access, satisfactory bandwidths for modems have increased to levels such as 28.8 kilobits per second transfer rates and higher. To facilitate such transfer rates, modems have become increasingly more sophisticated. Modern modems may employ sophisticated modulation techniques to transfer a substantial number of bits using sophisticated encoding structures. To facilitate high data rate transmissions, modems and wireless transceivers must efficiently utilize available bandwidth.
FIG. 1 represents a prior art configuration of a wireless transceiver 106 capable of wireless transmission to a wireless base station 108. Because wireless transceivers 106 typically facilitate voice transmission, a wireless modem 104 must be coupled to wireless transceiver 106 to facilitate modulation of input data 102 for transmission across an analog channel. Wireless base station 108 includes a transceiver 110 for modulating/demodulating the transmission carrier. Output signal 114 may then be routed through traditional network such as Public Switched Telephone Network (PSTN) or Integrated Services Digital Network (ISDN) networks to a recipient user for demonstration of output data 114 by a modem 112.
As discussed above, wireless transceiver 106, because of its substantial usage for voice transmission, has generally been optimized or adapted for transmission of voice information. A spectral analysis of voice information reveals that voice frequencies have higher amplitudes at the lower frequencies and taper-off as frequency increases. Wireless transceivers adapted for voice transmission have recognized this characteristic and have, therefore, incorporated a pre-emphasis module 116 to boost higher frequency amplitudes prior to transmission over a wireless network. Such a pre-emphasis processing of higher frequencies improves their tolerance for noise contamination resulting from the transmission process. Additionally, a limiter 118 clips any extraneously high amplitude levels of a voice-like signal. An RF transceiver 120 modulates the RF carrier frequencies with the voice signal for propagation via an antenna 122 across a wireless communication channel 124.
Wireless base station antennae 126 then captures the propagating transmission and delivers it to an RF transceiver 128 for demodulation of the transmit carrier. The carrier demodulated signal is then processed through a de-emphasizer module 130 for reducing the artificially increased amplitude levels of the higher frequencies of the transmitted voice information.
A spectral analysis of data information reveals that data maintains a constant or flat amplitude across the frequency spectrum. Early systems provided data having a flat spectrum directly to the input of wireless transceiver 106. Data was then pre-emphasized in pre-emphasis module 116, thus enhancing the amplitude levels of the higher frequencies. Such further enhancements to higher frequency amplitudes required that amplitudes exceeding a transmission threshold be clipped by limiter 118 to prevent out of bandwidth transmissions. Such clipping creates non-linear distortion which greatly facilitates the introduction of transmission errors. Alternatively, the amplitude of the data delivered to transceiver 106 could be reduced sufficient that the amplitude of the signal out of pre-emphasizer 116 would be low enough that it is not clipped by limiter 118. Such reduction of amplitude results in a lower signal-to-noise ratio, and hence a higher susceptibility to errors, which leads to lower data throughput. Therefore, pre-emphasis/de-emphasis processing which enhances and facilitates the transmission of voice information, degrades and renders susceptible to errors data transmission via the same transmission conduit of wireless transceiver 106.
Prior art configurations have attempted to remedy this situation by including within modem 104 a de-emphasis module 132 to pre-condition modulated input data prior to delivering such data to wireless transceiver 106. Input data 102 is first modulated by modulator 136 and presents modulated input data to de-emphasis module 132 for de-emphasizing or reducing the amplitudes of the higher frequency components of input data 201 following modulation. Such de-emphasized modulated data when presented to pre-emphasis module 116 becomes again emphasized in the higher frequencies thus giving the appearance of the original flat-spectrumed input data 201. Such prior art configurations of positioning a de-emphasis module 132 subsequent to modulator 136 have been implemented generally using a dedicated higher frequency filter required by the modulated characteristics of the signal undergoing such processing. Requiring a dedicated higher frequency capable hardware filter increases the complexity, size, weight, and costs of wireless modem 104 while potentially reducing the reliability due to the added components. When such de-emphasis processing of de-emphasis module 132 occurs in an existing component such as a digital signal processor, a significant number of instruction cycles are required to process the modulated baseband input data. When DSP instruction cycles are borrowed for collateral processing such as de-emphasis processing, overall throughput of modem 104 may be dramatically affected.
Thus, what is needed is a method and system for improving a data transmission rate of baseband data across a wireless network via a wireless transceiver that is adapted for voice transmissions.